brand-x skrev:
Baard !
Den er grei...

mat må man ha....
mvh
Kjell P..
Ok - dette blir litt OT i forhold til trådstarter. Men emne er jo klasse A - lettere å få tilgivelse enn tillatelse kanskje

Har ikke så mye eget å komme med, bare kildehenvisning fra:
Current Source Amplifiers and Sensitive Drivers
http://www.firstwatt.com/downloads/cs-amps-speakers.pdf
Nelson Pass har skrevet flere artikler rundt tema fullrange speaker og low power class-A og har sogar utviklet en egen serie med SS klasse-A forsterker for best mulig utnytte fordelene med fulltone-elementer. Litt av bakgrunnen var også en undring over at transistorforsterkere (uavhengig av klasse) tradisjonelt har vært en dårlig match mot Lowther, Fostex etc..
Løsningen iflg. NP har for SS vært å gå fra voltage amplifiers til current source amplifiers
Er det mulig gjøre en SS klasse-A forsterkere stort enklere enn dette? F3: JFet forsterker på 10-15W
For de som ikke orker lese hele artikkelen har jeg sakset litt.
Bakgrunn:
I began playing with full-range drivers, those loudspeakers which deliver bass, midrange and treble from one single cone. In a number of ways, they dont measure as well as multiple specialized drivers particularly at the bottom and the top, but there is something aesthetically appealing about the simplicity of the idea and on many occasions, they manage to sound very good especially driven by tube amplifiers.
Most interesting are the full-range high-efficiency drivers that deliver the goods with only a watt or so.
Tube amplifiers seem to bring out the best in such drivers. They have more bottom end, a warmer, mellower mid and upper mid-range, and often more top octave. By comparison, the best solid-state state amplifiers make them sound more like transistor radios less bottom and a, occasionally strident upper midrange. If you are a solid-state kind of guy (like me) you start wondering how that could be, and if you are a tube aficionado, you smirk and say, I told you so. The solid-state guy probably starts fixing the response with a parametric equalizer, and the tube guy enjoys his music with a nice glass of wine.
Forklaring:
An input voltage causes the amplifier to deliver a proportional output current. Of course this same sort of thing would occur with an ordinary amplifier driving a pure resistance but a loudspeaker circuit is not purely resistive. It possesses numerous reactive elements, some due to inductance and capacitance in the electrical circuit, some from the reaction to motion of the voice coil in a complex mechanical system. Fed by a voltage amplifier, the current through the drivers voice coil is not directly or instantly proportional to the input to the amplifier. Ordinarily, loudspeakers are designed around this assumption but the piston model of loudspeaker design assumes that the acoustic output mirrors the acceleration of the voice coil/cone assembly over a specific range and this is reflected by the current through the voice coil.
The most precise way to develop that specific current is with a current-source amplifier. Such an amplifier ignores the impedances in series with the circuit, the resistance and inductance of the wire and voice coil and the back electromotive force (EMF) produced by the cone motion.
As I said, most speakers are designed around voltage sources but there are few instances where a current source can be used to advantage. One of the best ones is the category of full-range high-efficiency drivers.
Oppsummering:
Somewhere in the 1960s, the speaker/amplifier interface took a left turn and headed off to high-power voltage source amplifiers and speakers designed to lean on them for performance. A small group of iconoclastic cranks has stayed interested in these fossils and in the end, we have to recognize full-range high-efficiency speakers as offering elegance, charm and a different sort of quality.
Etterord:
Remember, you dont have to own a current-source amplifier to put this information to work. Placing R0 in series with the output of a powerful voltage-source amplifier instead of in parallel with a current source will give similar results. If R0 is 47 ohms or higher, you are going to want a big amp, say 300 watts, but in any case, be certain to use a high power resistor of 50 watts or more. That said, its all just entertainment and I hope it inspires some of you to have some fun.